Question

A cricket ball weighing $100\text{g}$ and moving with a speed of $20{\text{m s}}^{-1}$ strikes a bat and remains is contact with it for $0.1\text{s}$. The average force exerted by the ball on the bat is:

• A. $100\text{N}$
• B. $10\text{N}$
• C. $40\text{N}$
• D. $1\text{N}$

Answer 1

The correct option is C $40\text{N}$

Given,
Mass of the ball (m) = 100 g = 0.1 kg
Momentum of a body (p) is given by,
p = m x v
Momentum before impact = mass x inital velocity
$=0.1\times 20=2{\text{kg m s}}^{-1}$
After impact the ball will move with same velocity but in opposite direction,
Final velocity = - (Initial velocity)
So,
Momentum after impact
$=0.1\times -20=-2{\text{kg m s}}^{-1}$
$\therefore$ Change of momentum $=2-(-2)=4{\text{kg m s}}^{-1}$

Also,
Force equals change in momentum per unit time. So,
$\therefore$ Force $=\frac{\Delta \text{p}}{\Delta \text{t}}=\frac{4}{0.1}=40\text{N}$